The Eurasian (or Northern) Sparrowhawk (Accipiter nisus) is a small bird of prey in the family Accipitridae which includes many other diurnal raptors such as eagles, buzzards, harriers, and other sparrowhawks. Adult male Eurasian Sparrowhawks have bluish grey upperparts and orange-barred underparts; females and juveniles are brown above with brown bars below. The male is up to 25% smaller than the female – one of the largest differences between the sexes in any bird species.

It is a predator which specialises in catching woodland birds, but it can be seen in any habitat and often hunts garden birds in towns and cities. Male Eurasian Sparrowhawks tend to take tits, finches, and sparrows; females catch thrushes and starlings, but are capable of killing birds weighing 500 g (17 oz) or more. Eurasian Sparrowhawks breed in suitable woodland of any type.

This species is now one of the commonest birds of prey in Europe, although the population crashed after the Second World War. Organochlorine insecticides used to treat seeds before sowing built up in the bird population and the concentrations in Eurasian Sparrowhawks were enough to kill some outright and incapacitate others; affected birds laid eggs with fragile shells which broke during incubation.

TaxonomyWithin the Accipitridae family, the Eurasian Sparrowhawk is a member of the large genus Accipiter, which consists of small to medium-sized woodland hawks. Most of the Old World members of the genus are called sparrowhawks or goshawks.

The Eurasian Sparrowhawk was described by Linnaeus in his 18th century work, Systema Naturae, as Falco nisus, but moved to its present genus by French zoologist Mathurin Jacques Brisson in 1760. The current scientific name is derived from the Latin accipiter, meaning 'hawk' and nisus, the sparrowhawk. The Eurasian Sparrowhawk forms a superspecies with the Rufous-chested Sparrowhawk of eastern and southern Africa, and possibly the Madagascar Sparrowhawk.

Six subspecies are generally recognised:1. Accipiter nisus nisus, the nominate subspecies, was described by Linnaeus in 1758. It breeds in Europe and west Asia to western Siberia and Iran; northern populations winter south to the Mediterranean, north-east Africa, Arabia and Pakistan. 2. Accipiter nisus nisosimilis was described by Samuel Tickell in 1833. This subspecies breeds in central and eastern Siberia east to Kamchatka and Japan, and south to north China; it is wholly migratory, wintering from Pakistan and India eastwards through South-East Asia and south China to Korea and Japan, with some even reaching Africa. 3. Accipiter nisus melaschistos was described by Allan Octavian Hume in 1869. It breeds in mountains from Afghanistan through the Himalayas and southern Tibet to western China, and winters in the plains. It is longer tailed than nisosimilis, is larger, dark slate-coloured on its upperparts, and with more distinct rufous barring on the underparts. 4. Accipiter nisus wolterstorffi was described by Otto Kleinschmidt in 1900. It is resident in Sardinia and Corsica, smaller, darker on the upperparts and more barred. 5. Accipiter nisus granti was described by Richard Bowdler Sharpe in 1890.[7] It is confined to Madeira and the Canary Islands, small and dark.[10] 6. Accipiter nisus punicus was described by Erlanger in 1897. It is resident in north-west Africa north of the Sahara. It is very similar to nisus, being large and pale.

DescriptionThe Eurasian Sparrowhawk is a small bird of prey with short, broad wings and a long tail, both adaptations to manoeuvring through trees. Females can be up to 25% larger than males – the largest difference between the sexes in any bird species, although Ferguson-Lees and Christie report that "nine other mainly bird-eating Accipiters have the difference even more marked." When females are larger than males, it is known as reverse sexual dimorphism; this is unusual in higher vertebrates but typical in birds of prey.

The adult male is 29–34 cm (11–13 inches) long with a 59–64 cm (23–25 inches) wingspan, and is slate-grey above (though some are more bluish). The underparts are finely barred reddish, looking plain orange from a distance; his irides are orange-yellow or orange-red. He weighs between 131–180 g (5–6 oz). The female is much larger at 35–41 cm (14–16 inches) long with a 67–80 cm (26–31 inch) wingspan, weighing between 186–345 g (7–12 oz). She has dark brown, or greyish-brown, upperparts and brown-barred underparts, and bright yellow to orange eyes. The juvenile is warm brown above, with rusty fringes to the upperparts and coarsely barred or spotted brown below, with pale yellow eyes; its throat has dark streaks and lacks a mesial (midline) stripe.

The Eurasian Sparrowhawk's pale underparts and darker upperparts are an example of countershading, which helps to break up the bird's outline. Countershading is exhibited by birds of prey which hunt birds and other fast-moving animals. The horizontal barring seen on adult Eurasian Sparrowhawks is typical of woodland-dwelling predatory birds, while the adult male's bluish colour is also seen in other bird-eating raptors like the Peregrine Falcon, Merlin, and other Accipiters. Old English folk names for this species include Blue Hawk, referring to the adult male's colouration, as well as Spar Hawk, Spur Hawk and Stone Falcon.

The Eurasian Sparrowhawk's small bill is used for plucking feathers and pulling apart prey, rather than killing or cutting. Its long legs and toes are an adaptation for catching and eating birds. The outer toe is "fairly long and slender"; the inner toe and back toe are relatively short and thick. The middle toe is very long and can be used to grasp objects – a protuberance on the underside of the toe means that the digit can be closed without leaving a gap.

The flight is a characteristic "flap-flap-glide", with the glide creating an undulating pattern. This species is similar in size to the Levant Sparrowhawk but bigger than the Shikra; the male is only slightly larger than the Merlin. Because of the overlap in sizes, the female can be confused with the similarly-sized male Northern Goshawk, but lacks the bulk of that species. Eurasian Sparrowhawks are smaller, more slender and have shorter wings, a square-ended tail and fly with faster wingbeats. A confusion species in China is the Besra, though A. n. melaschistos is considerably larger.

In Great Britain, Eurasian Sparrowhawks living further north are bigger than their more southerly counterparts, with wing length (the most reliable indicator of body size) increasing by an average of 0.86 mm (0.034 in) in males, and 0.75 mm (0.030 in) in females, for each degree further north.

Lifespan and demographyThe oldest recorded Eurasian Sparrowhawk in Europe was a bird found dead in Denmark which, because it had been ringed, was known to be 20 years, 3 months old. The typical lifespan is four years. Data analysis by the British Trust for Ornithology shows that the proportion of juveniles surviving their first year of life is 34%; adult survival from one year to the next is 69%. Birds in their first year of life weigh less than adults, and are especially light in the two months after reaching independence. There is probably high mortality, especially for young males, during this time. Observations from Newton's study of Eurasian Sparrowhawks in southern Scotland suggested that greater mortality in young male birds may have been because of their smaller size and the smaller size of their prey, which meant that they "could last less long between meals." Their size also meant that their range of prey was restricted. It was estimated that a female Eurasian Sparrowhawk weighing an average amount could survive for seven days without feeding – three days longer than a male.

A study of female Eurasian Sparrowhawks found "strong evidence" that their rate of survival increased for the first three years of life, and declined for the last five to six years. Senescence (ageing) was the cause of the decline as the birds became older.

Distribution and habitatA widespread species throughout the temperate and subtropical parts of the Old World, the Eurasian Sparrowhawk has an estimated global range of between 100,000–1,000,000 km2 (38,000–380,000 miles2) and an estimated population of 1 million to 10 million birds; it is one of the most common birds of prey in Europe, along with the Common Kestrel and Common Buzzard. Although global population trends have not been analysed, numbers seem to be stable, so it has been classified as being of Least Concern by BirdLife International. The race granti, with 100 pairs resident on Madeira and 200 pairs on the Canary Islands, is threatened by loss of habitat, egg-collecting and illegal hunting, and is listed on Annex I of the European Commission Birds Directive. The Norwegian and Albanian populations are declining and, in many parts of Europe, Eurasian Sparrowhawks are still shot. However, such low level persecution has not affected the populations badly. In the UK, the population increased by 108% between 1970–2005, but saw a 1% decline over 1994–2006.

This species is common in most woodland types in its range and also in more open country with scattered trees. Eurasian Sparrowhawks prefer to hunt woodland edges, but migrant birds can be seen in any habitat. The increased proportion of medium-aged stands of trees created by modern forestry techniques have benefited the species, according to a Norwegian study. Unlike its larger relative the Northern Goshawk, it can be seen in gardens and in urban areas and will even breed in city parks.

Eurasian Sparrowhawks from colder regions of northern Europe and Asia migrate south for the winter, some to north Africa (some as far as equatorial east Africa) and India; members of the southern populations are resident or disperse. Juveniles begin their migration earlier than adults and juvenile females move before juvenile males. Analysis of ringing data collected at Heligoland, Germany, found that males move further and more often than females; of migrating birds ringed at Kaliningrad, Russia, the average distance moved before recovery (when the ring is read and the bird's whereabouts reported subsequently) was 1,328 km (825 miles) for males and 927 km (576 miles) for females.

A study of Eurasian Sparrowhawks in southern Scotland found that ringed birds which had been raised on "high grade" territories were recovered in greater proportion than birds which came from "low grade" territories. This suggested that the high grade territories produced young which survived better. The recovery rate also declined with increased elevation of the ground. After the post-fledging period, female birds dispersed greater distances than did males.

Food and feedingThe Eurasian Sparrowhawk is a main predator of smaller woodland birds. It hunts by surprise attack, using hedges, tree-belts, copses, orchards and other cover near woodland areas; their choice of habitat is dictated by these requirements. Eurasian Sparrowhawks do not hesitate to make use of gardens in built-up areas and take advantage of the prey found there.

It waits, hidden, for birds to come near, then breaks cover and flies out fast and low. A chase may follow, with the hawk even flipping upside-down to grab the victim from below or following it on foot through vegetation. It can "stoop" onto prey from a great height. Ian Newton describes seven modes of hunting used by Eurasian Sparrowhawks:

Short-stay-perch-hunting

High soaring and stooping

Contour-hugging in flight

Still-hunting

Low quartering

Hunting by sound

Hunting on foot

Only 10% of Eurasian Sparrowhawk attacks result in prey being caught. Male Eurasian Sparrowhawks regularly kill birds weighing up to 40 g (1.5 oz) and sometimes up to 120 g (4 oz); females can tackle prey up to 500 g (17 oz) or more. The weight of food consumed by adult birds daily is estimated to be 40–50 g (1.4–1.7 oz) for males and 50–70 g (1.7–2.5 oz) for females. During one year, a pair of Eurasian Sparrowhawks could take 2,200 House Sparrows, 600 Common Blackbirds or 110 Wood Pigeons. Species that feed in the open, far from cover, or are conspicuous by their behaviour or coloration, are taken more often by Eurasian Sparrowhawks. For example, Great Tits and House Sparrows are vulnerable to attack. Eurasian Sparrowhawks may account for more than 50% of deaths in certain species, but the extent varies from area to area.

Males tend to take tits, finches, sparrows and buntings; females often take thrushes and starlings. Larger quarry (such as doves and magpies) may not die immediately but succumb during feather plucking and eating. More than 120 bird species have been recorded as prey and individual Eurasian Sparrowhawks may specialise in certain prey. The birds taken are usually adults or fledglings, though chicks in the nest and carrion are sometimes eaten. Small mammals, including bats, are sometimes caught but insects are eaten only very rarely.

Small birds are killed on impact or when squeezed by the Eurasian Sparrowhawk's foot, especially the two long claws. Victims which struggle are "kneaded" by the hawk, using its talons to squeeze and stab. When dealing with large prey species which peck and flap, the hawk's long legs help. It stands on top of its prey to pluck and pull it apart. The feathers are plucked and usually the breast muscles are eaten first. The bones are left, but can be broken using the notch in the bill. Like other birds of prey, Eurasian Sparrowhawks produce pellets containing indigestible parts of their prey. These range from 25 to 35 mm (1.0–1.4 inches) long and 10–18 mm (0.4–0.7 inches) wide and are round at one end and more narrow and pointed at the other. They are usually composed of small feathers, as the larger ones are plucked and not consumed.

During hunting, this species can fly 2–3 km (1.2–1.9 miles) per day. It rises above tree level mostly to display, soar above territory and to make longer journeys. A study in a forested area of Norway found that the mean size of the home ranges was 9.2 kmฒ (3.5 milesฒ) for males, and 12.3 kmฒ (4.7 milesฒ) for females, which was larger than studies in Great Britain had found, "probably due to lower land productivity and associated lower densities of prey species in the [Norwegian study area]".

A study looked at the effect on the population of Blue Tits in an area where a pair of Eurasian Sparrowhawks began to breed in 1990. It found that the annual adult survival rate for the tits in that area dropped from 0.485 to 0.376 (the rate in adjacent plots did not change). The size of the breeding population was not changed, but there were fewer non-breeding Blue Tits in the population. In woodland, Eurasian Sparrowhawks account for the deaths of a third of all young Great Tits; the two alarm calls given by Great Tits when mobbing a predator, and when fleeing from a nearby hawk, are within the optimum hearing range of both prey and predator; however, the high-pitched alarm call given when a distant flying Eurasian Sparrowhawk is seen "can only be heard well by the tit."] Research carried out in Sussex, England, found that the impact of Eurasian Sparrowhawk predation on Grey Partridges was highest when the partridge density was lowest, while a 10-year study in Scotland found that Eurasian Sparrowhawks did not select the Common Redshanks they predated according to the waders' size or condition, probably because of the hawks' surprise-attack hunting technique.

Another study found that the risk of predation for a bird targeted by a Eurasian Sparrowhawk or Northern Goshawk increased 25-fold if the prey was infected with the blood parasite Leucocytozoon, and birds with avian malaria were 16 times more likely to be killed.

BreedingThe Eurasian Sparrowhawk breeds in well-grown, extensive areas of woodland, often coniferous or mixed, preferring that with structure neither too dense or too open, to allow a choice of flight paths. The nest can be located in the fork of a tree, often near the trunk and where two or three branches begin, on a horizontal branch in the lower canopy, or near the top of a tall shrub. If available, conifers are preferred. A new nest is built every year, with the male doing most of the work, close to that of the previous year and sometimes using an old Wood Pigeon nest as a base. The structure of loose twigs (up to 60 cm, or 2 feet, long) has an average diameter of 60 cm. When the eggs are laid, a lining of fine twigs or bark chippings is added.

During the breeding season, the adult male Eurasian Sparrowhawk loses a small amount of weight while feeding his mate before she lays eggs, and also when the young are large and require more food. The weight of the adult female is highest in May, when laying eggs, and lowest in August after the breeding cycle is complete. A study suggested that the number of eggs and subsequent breeding success are dependent on the female maintaining a high weight while the male is feeding her.

Sexual maturity is reached at between 1–3 years. Most Eurasian Sparrowhawks stay on the same territory for one breeding season, though others keep the same one for up to eight years. A change of mate usually triggers the change in territory. Older birds tend to stay in the same territory; failed breeding attempts make a move more likely. The birds which kept the same territories had higher nest success, though it did not increase between years; females which moved experienced more success the year after changing territory.

EggsThe background colour of the eggs changes from light blue to white on storage in collections. The eggs are pale blue with brown spots and each measure 35–46 x 28–35 mm (1.4–1.8 x 1.1–1.4 inches), and weigh about 22.5 g (0.8 oz) of which 8% is shell in a healthy egg. Usually a clutch of four or five eggs is laid. The eggs are generally laid in the morning with an interval of 2–3 days between each egg. If a clutch is lost, up to two further eggs may be laid that are smaller than the earlier eggs.

YoungThe altricial, downy chicks hatch after 33 days of incubation. After hatching, the female cares for and feeds the chicks for the first 8–14 days of life, and also during bad weather after that. The male provides food, up to six kills per day in the first week increasing to eight per day in the third and 10 per day in the last week in the nest, by which time the female is also hunting.

At between 24–28 days after hatching, the young birds start to perch on branches near the nest and take their first flight. They are fed by their parents for another 28–30 days after this, staying close to the nest while growing and practicing flying. The young hawks disperse after their parents stop provisioning them.] Though they receive the same amount of food, male chicks (roughly half the size of females) mature more quickly and seem to be ready to leave the nest sooner. In a study in the Forest of Ae, south-west Scotland, it was found that 21% of nestlings over two days old died, with the causes of death being starvation, wet weather, predation and desertion by the parents. The parasite Leucocytozoon toddi can be passed from parent to nestling at the nest, possibly because of the number of birds sharing a small space, thus allowing transmission.